This invention relates to a controllably bendable tube assembly, especially a borescope or endoscope of the type having a cable-actuated hollow steering section.
A borescope is generally characterized as an elongated flexible insertion tube with a viewing head at its distal or forward end, and a control section at its proximal end for controlling the bending at the distal end. In such a borescope, a bendable tube steering section is situated at the distal end adjacent to the viewing head. One or two pairs of control cables extend through the bendable tube section and the remainder of the insertion tube and connect with a steering control mechanism in the control section. One or both pairs of these cables are differentially displaced for bending the steering section to facilitate the inspection of a remote object.
A borescope is typically intended for visual inspection of an intricate mechanical assembly, such as a jet engine or turbine, where it would be difficult or impossible otherwise to view the assembly's internal elements. The borescope needs to be insertable into narrow, tortuous passageways, and must observe very delicate steering considerations.
It is necessary that cable slack be minimized to avoid slack or play in steering. Also, the compression load applied to the cable sheaths must be accurately maintained. Furthermore, the steering horizon for the control section should be aligned as closely as possible with the bending axis of the steering section, despite the cumulative alignment errors that may occur in assembly of the borescope.
An endoscope is typically inserted into a body cavity of a patient for visual inspection of tissues within the cavity. Because body passages such as esophagus, bronchia, and colon are narrow and tortuous, the steering section must be bent rather precisely, and as close to the viewing head as possible. Thus, cable tension must be limited and cable slack minimized as much as possible.
The opposing steering cables of each pair are required to displace to deflect the distal tip. The cables are differentially displaced , that is, as one cable is drawn into the control section, the other is released a like amount. However, the motion of one cable is not the exact opposite of the motion of the other. Also, coiling of the insertion tube can result in tensioning of both cables at the same time. For these and other reasons, there is a tendency for cables to stretch over time, leading to slop or play in steering, with ensuing loss of precision.
Moreover, it is difficult or impossible to maintain accurate adjustment of cable sheath forces during assembly. The usual, conventional installation of cable sheaths involves adjusting a threaded cable adjuster in a threaded bore in a carrier within the housing of the control section. There are lock nuts on the threads of the cable adjusters, and the lock nuts are tightened against the carrier to keep the adjuster in place. However, tightening of the lock nut frequently results in rotations of the cable sheath adjuster, and this results in loosening or overstressing the cable sheath.
Moreover, it is desirable to keep the axis of bending of the steering section aligned as closely as possible with the axis of the steering control mechanism of the control section. However, in conventional borescopes, some errors in alignment do exist within the control section, and these can accumulate over the numerous steps of assembly. Once the conventional probe device is assembled, it is difficult or impossible to adjust the tube orientation relative to the control section.